1 package org.apache.turbine.modules;
2
3 /* ====================================================================
4 * The Apache Software License, Version 1.1
5 *
6 * Copyright (c) 2001 The Apache Software Foundation. All rights
7 * reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 *
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
19 * distribution.
20 *
21 * 3. The end-user documentation included with the redistribution,
22 * if any, must include the following acknowledgment:
23 * "This product includes software developed by the
24 * Apache Software Foundation (http://www.apache.org/)."
25 * Alternately, this acknowledgment may appear in the software itself,
26 * if and wherever such third-party acknowledgments normally appear.
27 *
28 * 4. The names "Apache" and "Apache Software Foundation" and
29 * "Apache Turbine" must not be used to endorse or promote products
30 * derived from this software without prior written permission. For
31 * written permission, please contact apache@apache.org.
32 *
33 * 5. Products derived from this software may not be called "Apache",
34 * "Apache Turbine", nor may "Apache" appear in their name, without
35 * prior written permission of the Apache Software Foundation.
36 *
37 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48 * SUCH DAMAGE.
49 * ====================================================================
50 *
51 * This software consists of voluntary contributions made by many
52 * individuals on behalf of the Apache Software Foundation. For more
53 * information on the Apache Software Foundation, please see
54 * <http://www.apache.org/>.
55 */
56
57 // Java Core Classes
58 import java.util.Vector;
59
60 // Turbine Utility Classes
61 import org.apache.turbine.TurbineConstants;
62 import org.apache.turbine.services.resources.TurbineResources;
63 import org.apache.turbine.services.TurbineServices;
64 import org.apache.turbine.services.assemblerbroker.AssemblerBrokerService;
65 import org.apache.turbine.util.ObjectUtils;
66 import org.apache.turbine.util.RunData;
67
68 // ECS
69 import org.apache.ecs.ConcreteElement;
70
71 /***
72 * The purpose of this class is to allow one to load and execute
73 * Screen modules.
74 *
75 * @author <a href="mailto:mbryson@mont.mindspring.com">Dave Bryson</a>
76 * @version $Id: ScreenLoader.java,v 1.1.1.1 2001/08/16 05:08:31 jvanzyl Exp $
77 */
78 public class ScreenLoader extends GenericLoader
79 {
80 /*** The single instance of this class. */
81 private static ScreenLoader instance = new ScreenLoader(
82 TurbineResources.getInt(TurbineConstants.SCREEN_CACHE_SIZE, 50));
83
84 /***
85 * These ctor's are private to force clients to use getInstance()
86 * to access this class.
87 */
88 private ScreenLoader()
89 {
90 super();
91 }
92
93 /***
94 * These ctor's are private to force clients to use getInstance()
95 * to access this class.
96 */
97 private ScreenLoader(int i)
98 {
99 super(i);
100 }
101
102 /***
103 * Adds an instance of an object into the hashtable.
104 *
105 * @param name Name of object.
106 * @param screen Screen to be associated with name.
107 */
108 private void addInstance( String name, Screen screen )
109 {
110 if ( cache() )
111 this.put( name, (Screen) screen );
112 }
113
114 /***
115 * Attempts to load and execute the external Screen. This is used
116 * when you want to execute a Screen which returns its output via
117 * a MultiPartElement instead of out the data.getPage() value.
118 * This allows you to easily chain the execution of Screen modules
119 * together.
120 *
121 * @param data Turbine information.
122 * @param name Name of object that will execute the screen.
123 * @exception Exception a generic exception.
124 */
125 public ConcreteElement eval( RunData data, String name )
126 throws Exception
127 {
128 // Execute screen
129 return getInstance(name).build(data);
130 }
131
132 /***
133 * Attempts to load and execute the Screen. This is used when you
134 * want to execute a Screen which returns its output via the
135 * data.getPage() object.
136 *
137 * @param data Turbine information.
138 * @param name Name of object that will execute the screen.
139 * @exception Exception a generic exception.
140 */
141 public void exec( RunData data, String name )
142 throws Exception
143 {
144 this.eval( data, name );
145 }
146
147 /***
148 * Pulls out an instance of the object by name. Name is just the
149 * single name of the object.
150 *
151 * @param name Name of object instance.
152 * @return A Screen with the specified name, or null.
153 * @exception Exception a generic exception.
154 */
155 public Screen getInstance(String name)
156 throws Exception
157 {
158 Screen screen = null;
159
160 // Check if the screen is already in the cache
161 if ( cache() && this.containsKey( name ) )
162 {
163 screen = (Screen) this.get( name );
164 }
165 else
166 {
167 // We get the broker service
168 AssemblerBrokerService ab =
169 (AssemblerBrokerService)TurbineServices.getInstance()
170 .getService (AssemblerBrokerService.SERVICE_NAME);
171
172 try
173 {
174 // Attempt to load the screen
175 screen = (Screen) ab
176 .getAssembler(AssemblerBrokerService.SCREEN_TYPE,name);
177 }
178 catch (ClassCastException cce)
179 {
180 // This can alternatively let this exception be thrown
181 // So that the ClassCastException is shown in the
182 // browser window. Like this it shows "Screen not Found"
183 screen = null;
184 }
185
186 if (screen == null)
187 {
188 // If we did not find a screen we should try and give
189 // the user a reason for that...
190 // FIX ME: The AssemblerFactories should each add it's
191 // own string here...
192 TurbineResources/index.html">Vector packages = TurbineResources
193 .getVector(TurbineConstants.MODULE_PACKAGES);
194 ObjectUtils.addOnce( packages,
195 GenericLoader.getBasePackage() );
196
197 throw new ClassNotFoundException (
198 "\n\n\tRequested Screen not found: " + name +
199 "\n\tTurbine looked in the following " +
200 "modules.packages path: \n\t" + packages.toString() + "\n");
201 }
202 else if ( cache() )
203 {
204 // The new instance is added to the cache
205 addInstance( name, screen );
206 }
207 }
208 return screen;
209 }
210
211 /***
212 * The method through which this class is accessed.
213 *
214 * @return The single instance of this class.
215 */
216 public static ScreenLoader getInstance()
217 {
218 return instance;
219 }
220 }
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